1. Field of the Invention
This invention relates generally to wireless monitoring systems and particularly to such systems adapted to monitor the location of movable items such as people, animals or merchandise. More particularly, this invention relates to a wireless transmitter attached to each item and a base station monitoring multiple items, providing out of range alarms and doubling as a finding device.
2. Description of Related Art
Geriatric patients often move about freely within the boundaries of a resident hospital, but some could endanger themselves and become lost and unable to find their way home if they wander outside the grounds. Likewise, pets straying too far from a home location sometimes get lost or stolen. Expensive retail merchandise susceptible to shoplifting can be spirited away and if small enough hidden in the thief's pocket or packages, thereby deterring thorough investigation based on suspicion alone. Horror stories abound of children or scuba divers on tours being left behind because an improper head count overlooked their absence.
Numerous prior art devices and systems provide means for monitoring the location and status of movable items, but most are too expensive and complex for practical use in many of the above circumstances. Systems designed for patients potentially needing immediate medical attention provide a base station and portable transceivers which trigger an alarm, either manually by a distressed patient or automatically by a sensor monitoring body functions such as breathing or pulse. The base unit then alerts help on the premises or contacts emergency response services such as police or paramedics to come to the patient's assistance. Such systems typically involve patient signaling options and transceiver functions in the patient-worn device and in the base unit, making them complex and expensive and reducing the applications in which they are practical.
Other less expensive perimeter monitoring systems rely on passive unit-carried devices which set off an alarm as the unit passes a perimeter sensor, like retail shoplifting detection systems, but which provide no distance and direction capabilities for finding missing units. A simple system which detects unit movement beyond a given perimeter or distance could find wide uses in diverse markets.